Thanks for your enquiry.
Attorneys appointed jointly and severally can act and make decisions independently of any other Attorneys, as well as together with them. Therefore any one Attorney could apply to register the EPA alone. In this situation the OPG (the Office of Public Guardian) would only accept the application if all the other Attorneys had been properly notified of the application and given the opportunity to object to it.
Therefore, if your Brother were to register the Power in his ole name, you can object to this, and the OPG will then register the Power in favour of both you Attorneys.
I would certainly hope that your Brother would play by the book and notify you of any intended registration he is making, but it wouldn't do you any harm in writing to the OPG now setting out your concerns so they have something on record were your Brother not to notify you and proceed with the registration. Alternatively, you may wish to notify your Brother of what I have said above.
I hope this answers your question.
Where the Attorneys have acted together in deciding to register